Archive for ◊ September, 2011 ◊

That title may make my spam-comment filter work overtime. Anyway, this post continues the discussion of managing figure in wood. Let’s look at the orientation of the annual rings in the rectangular blanks from which curved legs will be cut. Short sections of Douglas fir will be used to illustrate the principles.

All of this refers to legs which curve in three dimensions (planes). The curves may be cut on all four faces (e.g., a cabriole leg) or just two adjacent faces. Legs in which the curves are cut only on two opposite faces are curved in only two dimensions (picture the leg sandwiched between two flat sheets of plywood) and are a somewhat different matter. Bent lamination legs are an entirely different matter. Please do not ask me about legs which alter the time-space continuum.

The photo above shows the three possible basic orientations.The dot on the end grain indicates the inside corner of the legs. The two faces adjacent to this corner usually each have a flat portion where the aprons are attached with mortise and tenon joints.

In the three legs, from left to right, consider the endgrain patterns:

The annual rings are approximately parallel to one face and perpendicular to the other, producing one flatsawn face and one quartered face.

The annual rings are approximately 45° to all four faces and run “across” the inside corner.

The annual rings are approximately 45° to all four faces but run parallel to an axis from the inside corner to the outside corner.

For simplicity, I cut the curves into two adjacent faces. The effects would be the same if curves were cut into all four faces such as in a cabriole leg.

Let’s look at the results.

The leg on the left is bad news. The irregular figure produced by cutting a curve into the flatsawn face is unpleasant in itself, and the inconsistent figure among the faces distracts from the shape of the leg.

The middle leg is an improvement but, to my eye, the figure lines fight the curves of the legs. There is too much run-on and run-out of the annual ring lines.

I like the leg on the right. By cutting the blank from approximately 45̊ riftsawn stock and orienting the growth rings in this way relative to the inside corner, a good lookin’ leg arises. The shape of the leg (though uninteresting in this example) coordinates with the figure.

Here are closer views:

Note that another disadvantage of the leg on the left is the exaggerated consequence of a small knot intersecting the cut line. Small pin knots, such as are common in cherry, can be difficult to avoid, but the middle leg demonstrates that they will have much less consequence with that grain orientation.

It is hard to find a thick, purely riftsawn board from which to make leg blanks, but most fairly wide flatsawn boards contain some effectively riftsawn stock toward the sides. I examine the end grain and face grain and carefully select the best sections of such boards. I pay attention to the straightness of the figure along the length of the board, recutting the edge to “straighten” the figure lines if necessary. I also try to somewhat coordinate bends in the figure with bends in the leg design.

Of course, you can choose however you like to use figure, but the key is to be aware of it and manage it. Making your design and the beauty of the wood work together, each enhancing the other, can bring class, beauty, and quality to your woodworking projects.

Wood has figure that was created from life, which, in turn, helps bring life to a creation in wood. Throughout designing a piece, choosing wood, and building, I want to make the most of what the wood has to offer so a synergy develops between the design and the wood. This is not aluminum, Corian, or clay upon which a design is imposed; this is wood!

When cutting curves in wood, it is helpful to predict how the figure will change. The figure should work with, not fight, the contours of the piece. The interpretation of that task is subjective but it pays to be aware of and work skillfully with the figure. (Bent lamination, by the way, is a different matter.)

Here is a visual guide to some of the issues that arise in curved work. I used home center Douglas fir which has obvious figure lines created by the large difference between the earlywood and latewood. This is for purpose of illustration, it is not meant to be pretty.

In the photo above and the next two below, a concave curve (marked on the top surface) cut into the rift face causes the figure to bend. The end grain is emphasized with pen lines to show that the annual ring lines go downward as you go deeper into the wood. Thus, the concave curve creates a smiley bend from the straight face. A convex curve would do the opposite.

Below is the result if we started with the block with the opposite face on top. (I just turned the same block upside down.)

Now let’s cut a similar curve into a nearly-flat-sawn face. The end grain lines meet the face at an extreme angle and so the figure changes rapidly as we cut the depth of the curve. The result is, to my eye, unattractive. Some of the figure lines run off the resultant face at the bottom and jump on at the top.

Now let’s cut the curve into the quartered face. Since the annual ring lines meet the face at about 90̊, there is almost no shift in the direction of the figure after the curve is cut.

Of course, many other variables come into play, including the depth and consistency of the curves, and their placement in the piece. None of this would matter much in basswood which is nearly absent in figure.

The main ideas:

appreciate that the figure changes as curves are cut into wood

it is helpful to be able to generally predict how the figure will change

Once a machine woodworking procedure starts, any unexpected event will occur suddenly, probably too quickly for you to react. At that point, your defense is whatever margins of safety, such as guards and hand clearances, that have been built into the setup and come into play after the mishap. You have to hope they are adequate to prevent injury.

The safest way to use a woodworking machine is to know, before starting, exactly what is about to happen. It should be a completely predictable operation. We know the machine itself will operate in a fully predictable manner (the blade or bit spins), and so your job is to thoroughly understand and control the interactions among you, the wood, and the machine. You must understand all the forces at work. In short, don’t hit the start switch if your mind harbors doubts!

Of course, still use the guards and clearances.

2. Cut or throw?

A machine blade or cutter, given the opportunity, will always throw the wood rather than cut it. You must deny the machine that opportunity by restricting the movement of the wood, and ensure that it has the capacity to cut the wood. Using hand-held power tools, it may be the tool itself, with your hands still holding it, that gets kicked.

All of the following mishaps, among many more, are essentially a cutter throwing the work piece because the operator gave the machine an alternative to cutting it:

Table saw kickback – the absence of a splitter/riving knife allows the kerf to pinch the rising blade which grips and violently throws the wood.

Thickness planer kickback – a short board is freed from the infeed roller before reaching the outfeed roller so the blades grab and eject the unrestricted wood.

Drill press – the rim of a bit, such as a large diameter Forstner, snags an unclamped work piece and throws it, or worse, pulls in the hand that is trying to hold it. Re-entering a hole with a spinning bit increases the chance of this disaster.

Bandsaw – wood held above the table surface is presented to a coarse tooth blade and gets slammed to the table, drawing the worker’s hands with it, possibly into the blade.

Router table – uncontrolled climb cutting (feeding the work piece in the direction of the cutting edge rotation) zooms the wood across the table, possibly carrying the woodworker’s hands into the cutter.

Well, I’m getting uneasy just writing these scenarios. Of course, these two concepts are just part of safe practice, and there are many more ways to get hurt with machines. However, keeping these two basic principles in mind – and in action – will go a long way toward using machines safely.

When I want an absolutely reliable reference measuring tool, I reach for a Starrett. It’s that simple.

We’ve all had our frustrations with tools that seemed promising when new but proved to be deficient in design or construction and thus do not perform. I particularly avoid tools that are unnecessarily complicated or are merely solutions chasing a problem. Worst of all are tools that are made just to be pretty. On the other hand, don’t get me wrong, there are some great small-scale toolmakers out there making high quality, useful, and often innovative products.

Reliable primary references for straight and square are necessities in the shop – specifically, a straightedge at least 24″ long and a combination square (a large machinist square is a more expensive and less versatile alternative). Don’t skimp on quality for these; they are lifetime tools. Get Starretts and be done with it. (A flat reference, such as a granite surface plate, though not a must, is also helpful and can be had economically.) My Starrett tools include a 24″ straightedge, a combination square with a hardened head and 12″ and 18″ blades, a 6″ adjustable square, and several others that would be considered more optional than basic.

The integrity of most shop procedures and tools can be traced to verifications using these reference tools. Examples are a flat jointer table with a square fence, the soles of handplanes, a table saw crosscut jig, shop-made jigs, and so forth. Things such as these allow you to start a project on a reliable basis rather than dealing with fundamental inaccuracies that will be carried like an infection through the building process.

Top grade straight and square reference tools are like the Constitution of your shop and you’re the Supreme Court.

Starrett is a solid American company with a proud history, and is technologically current and innovative. They continue to manufacture most of their precision tools at their Athol, Massachusetts plant, working to unsurpassed tolerances. Every one of their measuring tools that I own or have seen has been exquisitely well finished. A Starrett is a mensch at the bench.